The present invention relates to casing hangers for supporting and sealing a string of casing in a wellhead.
In a typical oil or gas well, a string of casing is suspended from a load shoulder in wellhead by a casing hanger. The casing hanger has a lower ring that lands on the load shoulder, and a slip assembly grasps the string of casing. In one type of casing hanger, the weight of casing transmits through an elastomeric seal to a lower ring and to the load shoulder. The weight of the casing compresses the elastomeric seal axially and causes it to extrude radially into sealing contact with the casing string and the inner diameter of the wellhead.
Generally, the weight of the casing string is more than is needed to energize the seal, and the excess force can damage the seal. Therefore, prior art casing hangers incorporate a stop mechanism to limit the axial compression of the elastomeric seal and support the weight of the casing after the seal is energized.
One prior art casing hanger uses spacers which freely float within vertical holes in the seal. The spacers have a height less than the height of the seal, but are sized to transfer the load when the seal is compressed enough to seal the casing and casing head.
The present invention is drawn to a casing hanger for hanging and sealing a string of casing in a wellhead having a load shoulder therein. The casing hanger has a lower ring for landing on the load shoulder, the lower ring having an upward facing surface. A seal is positioned on the lower ring. The seal energizes when compressed axially to seal the casing to the wellhead. The seal has a plurality of circumferentially spaced holes. A slip assembly for gripping the casing has a downward facing surface that transmits downward forces from the weight of the casing to the seal to axially compress and energize the seal. Stop members are located in the holes in the seal and rigidly secured to one of the upward and downward facing surfaces to limit the compression of the seal to a predetermined amount.